In recent years, disposable articles, including medical and sanitary articles, etc., have widely used elastic material to improve the fit to the human body. Particularly, infant articles utilize an elastic sheet and a non-woven fabric composite much more frequently than an elastic sheet alone. In the elastic sheet and the non-woven fabric composite, the elastic sheet exhibits elastic properties and the non-woven fabric provides improved surface structure and reinforcement of the elastic sheet.
A typical example of such an elastic composite is a three-layer composite called S.M.S. (spunbonded/meltblown/spunbonded) which is disclosed in U.S. Pat. Nos. 4,663,220; 4,652,487; and 4,720,415. This composite is manufactured by a method called S.B.L. (Stretch-Bonded Laminate) wherein the elastic sheet is first stretched and is in its stretched state bonded to the non-woven fabric to form the composite upon release. The composite manufactured in accordance with this method has a stable range of elasticity and neither expands beyond the range nor breaks during normal use since its expansion limit corresponds to its stretched range during manufacture. However, the composite disadvantageously uses more of the non-woven fabric than may be necessary and is bulky so that it is not well-suited for high-speed commercial production.
Japanese Patent No. 4-281059 also discloses a method for directly entangling fibers into an elastic net, which, however, is costly. In order to remedy these drawbacks, an attempt (EPC No. 556,749) has been made to bond an elongatable non-woven fabric to an elastic film on line to form a composite of channel-like construction.
Japanese Utility Model No. 3-39509 discloses an elastic composite which is constructed by hydro-entangling a web comprising staple fibers and a non-woven fabric directly formed of thermoplastic elastomers. In order for the composite to have stretchability of higher than 70%, the web includes fibers which slightly crimp upon application of heat or which split into fibers of finer than 1 denier.
The above conventional composites are capable of expanding over a wide range from a breaking point of the non-woven fabric to a breaking point of the elastic sheet. Their critical points however create difficulty in designing products and defining its specifications. It also leaves users with insufficient knowledge of the proper use since they do not know at what point the composite breaks.